MolluscIreland - land and freshwater
  • Gyraulus (Armiger) crista (Linnaeus 1758) Nautilus ramshorn
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Gyraulus (Armiger) crista
© Dr Roy Anderson

Map hosted by the National Biodiversity Data Centre, Waterford
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A tiny loosely coiled shell with body whorl below the rest to create a flat spire. Whorls are traversed by radial ridges which may form conspicuous narrow keels at regular intervals. Surface pale brown, glossy but often covered with deposits. Widespread.

Key characteristics

  • A tiny loosely coiled shell with a low, flat spire
  • Whorls convex with weak to very strong and regular radial ridges
  • The ridges may form points on the periphery creating narrow keels
  • Shell surface smooth, brown, slightly glossy but usually obscured by deposits
  • Body whorl bluntly margined below, mouth oval to slightly angular
  • (Technically it has always been difficult with planorbids to decide whether the raised whorls form a spire or an umbilicus! In these accounts the raised part is called (commonsensically) a spire even even though most experts regard it as an umbilicus)

Size

2-3 mm.

World Distribution

Spread across the northern part of the whole northern hemisphere. Distribution type: Circumpolar Wide-temperate (66).

Irish Distribution

Very widespread and locally common but much under-recorded because of its size.

Ecology

  • A species of clear, weedy conditions in still water habitats
  • Common in medium to very small habitats including sluggish streams, drains and marsh or fen pools
  • Occasionally found in very acid waters
  • Habitat size appears to be little impediment to this species - a thriving colony lives in a tiny ornamental pool (3m across) at the Lion's Gate, Mussenden Temple on the north Londonderry coast in water at best 2-3cm deep

Red List status

  • Least concern (lc).

Wikipedia link

Wikipedia page for Gyraulus crista

 Anderson, R., (2016). Gyraulus (Armiger) crista (Linnaeus 1758). [In] MolluscIreland.
http://www.habitas.org.uk/molluscireland/species.asp?ID=87 Accessed on 2017-10-22.